Semiconductor device with high dielectric constant insulating film and manufacturing method for the same

ABSTRACT

A semiconductor device has a substrate and a dielectric film formed directly or indirectly on the substrate. The dielectric film contains a metal silicate film, and a silicon concentration in the metal silicate film is lower in a center portion in the film thickness direction than in an upper portion and in a lower portion.

This is a Divisional of application Ser. No. 10/477,109, filed Nov. 10,2003. The entire disclosure of the prior application, application Ser.No. 10/477,109 is hereby incorporated by reference.

TECHNICAL FIELD

The present invention is relates to a semiconductor device and amanufacturing method for the same, and more particularly to thestructure of a semiconductor device with a high dielectric constantinsulating film such as a high-performance MOSFET(Metal-Oxide-Semiconductor Field-Effect Transistor) and a manufacturingmethod for the same.

BACKGROUND ART

A silicon oxide film has stability on processes and excellent insulationcharacteristic and is used as a gate insulating or dielectric film of aMOSFET. The thinner structure of the gate dielectric film is progressingwith the miniaturization of a semiconductor device in recent years. Itbecomes necessary from the viewpoint of the scaling law in thesemiconductor device that the gate length is equal to silicon oxide filmas the gate dielectric film is equal to or less than 1.5 nm. However, insuch a thinner dielectric film, tunnel current flowing through theinsulating film in application of a gate bias can not be ignored tosource/drain current. As a result, it becomes a big problem in superiorperformance and low power consumption in the MOSFET.

For this reason, the studies and developments are carried forward todecrease an effective thickness of the gate dielectric film and tosuppress the tunnel current into a permissible value in system design.In one method, by adding nitrogen into the silicon oxide film, thedielectric constant is increased compared with a pure silicon oxidefilm. In this way, the film thickness of the gate dielectric film isdecreased effectively (electrically) without decreasing the filmthickness physically. However, there is a limit in this method in thatthe high dielectric constant is achieved by adding the nitrogen to thesilicon oxide film. Also it is reported that the carrier mobilitydecreases due to electrical defects at the interface.

Moreover, for technique in the next generation that the miniaturizationof the device further progresses, it is tried to use a thin film ofmetal oxides having a relative dielectric constant equal to or more than10 or a silicate thin film of composite material of the above materialand silicon as the gate dielectric film in place of the silicon oxidefilm. As such high relative dielectric constant material, Al₂O₃, ZrO₂,and HfO₂ oxide of the rare earth element such as Y₂O₃, and oxide of thelanthanoid system rare earth element such as La₂O₃ are studied ascandidacy materials. This is on the basis of that the thicker gatedielectric film can be achieved to prevent the tunnel current whilekeeping the inversion capacitance in accordance with the scaling law,even though the gate length is made small, if these high relativedielectric constant films are used. It should be noted that when it issupposed that the gate dielectric film is a silicon oxide filmregardless of the kind of material of the gate insulator, the filmthickness of the insulating film calculated from the gate capacitance iscalled an equivalent oxide thickness (EOT). That is, when the relativedielectric constants of the dielectric film and the silicon oxide filmare ∈h and ∈o respectively, and the thickness of the dielectric film isdh, the equivalent oxide thickness de is obtained from the followingequation.de=dh(∈o/∈h)It shows that a thick insulating film can be equivalent to a thinsilicon oxide film if the material has a dielectric constant ∈h largecompared with ∈o. For example, it is supposed that an insulating filmwith a large relative dielectric constant of ∈h=39 is used because therelative dielectric constant ∈o of the silicon oxide film is about 3.9.In this case, even if the dielectric film has the physical thickness of15 nm, the equivalent oxide thickness is 1.5 nm so that it is possibleto decrease the tunnel current sharply.

On the other hand, in case of development of the semiconductor memory,severe conditions are imposed on the structure of a capacitance elementto hold data as electric charge from the viewpoint of the reduction ofthe memory cell area. The technique to hold a sufficient amount ofelectric charge is required to a smaller cell area. In order to meetthese requests, a technique is developed to increase the dielectricconstant of the dielectric film of the capacitance element in additionto a technique to increase an element area by forming a minuteunevenness structure to the capacitance element.

As described above, in the development of the next generation MOSFET, itis considered to adopt high dielectric constant material as the gateinsulator, and the above-mentioned metal oxide film and the silicatefilm are expected as the high dielectric constant film. Ascharacteristics of these two candidate material films, the metal oxidefilm generally has a high dielectric constant and can reduce theequivalent oxide thickness dramatically.

However, these high dielectric constant films crystallize (take thepolycrystalline state) in a relatively low temperature region.Therefore, it is pointed out that the boundaries among the crystals (thecrystal grain boundaries) are generated to cause the degradation of theinsulation characteristic in these grain boundaries and thenon-uniformity of the film thickness through crystallization. For thisreason, a technical problem on application is in the securing of thermalstability as the gate dielectric film.

On the other hand, the dielectric constant of silicate material asternary system material of metal oxide and silicon is lower than themetal oxide material but higher than the silicon oxide film. Also, theabove-mentioned metal oxide material is easy to crystallize, whereassilicate material keeps an amorphous state in a high temperature range,and is not accompanied by the thermal change of the structure(characteristic). Therefore, the silicate material has predominance likethe conventional silicon oxide film. Moreover, a film composition can beset in a wide range. It is reported that the dielectric constantincreases by adding the metal element of % order to the silicon oxidefilm.

Also, in the application to the device for the high dielectric constantfilm, the electrical interface characteristics with the siliconsubstrate and the gate electrode material are important. Generally, theelectrical interface characteristics between the metal oxide film andthe silicon substrate are poor compared with those of the silicon oxidefilm and the silicon substrate and an interface defect density betweenthe metal oxide and the silicon substrate is equal to or more than thatof the silicon oxide film and the silicon substrate by one order. As themeans of improving the electrical interface characteristics, theeffectiveness of the metal silicate is pointed out.

In this way, attention is focused on the metal silicate material as theinfluential candidate material of the high dielectric constant gatedielectric film in the following generation. However, in application tothe MOSFET, the following problems exist.

First, the electrical interface characteristics between the siliconsubstrate and the gate electrode material needs to be more improved. Forthis purpose, it could be considered that a silicon composition in themetal silicate is increased to approximate to the interface structure ofthe silicon oxide film. On the other hand, it is known that thecrystallization temperature of the metal silicate decreases as the metalcomposition becomes high. Therefore, in order to achieve an excellentthermal stability, it is necessary to increase the silicon composition.However, the dielectric constant decreases with the increase of thesilicon composition in the silicate. Thus, the high dielectric constantof a gate dielectric film and the thermal stability have a trade-offrelation each other. That is, the metal silicate material has variousexcellent characteristics but is in the trade-off relation with settingof the film composition, as described above. Therefore, the proposal ofan optimal metal silicate material or the gate dielectric film structurein case of device application is demanded.

In addition to the above-mentioned pointing-out, another problem of thehigh dielectric constant gate insulating film is a band gap of insulatormaterial. Generally, there is a negative correlation between thedielectric constant and the band gap of the high dielectric constantmaterial, and the high dielectric constant material has a narrow bandgap. Therefore, when the valence band offset and the conduction bandoffset are small at the interface with the silicon substrate, carriersare thermally excited on the side of the silicon substrate or a gateelectrode and more electric current flows through the gate dielectricfilm.

The above technical problems of the gate dielectric film in the case ofthe application to MOSFET are essentially same with respect to thedielectric film of a capacitor cell, although the device generation isdifferent. The proposal of an insulating film structure with a highdielectric constant and thermal stability are demanded and excellentelectrical interface characteristics are also demanded.

In conjunction with the above description, a high dielectric constantfilm and a manufacturing method for the same are disclosed in JapaneseLaid Open Patent Application (JP-A-Heisei 5-275646). In this reference,the high dielectric constant film consists of the oxide of Ta and Hf ashigh dielectric constant materials and has a composition in the rangethat the mole ratio of elements is shown in the following equation.0.01≦Hf/(Ta+Hf)≦0.4A substrate is located in a vacuum chamber, source gases are introducedinto the vacuum chamber, and energy is applied from outside to excitethe source gases. Thus, the high dielectric constant film isvapor-deposited on the substrate. Ta source gas, Hf source gas, andoxygen containing gas are used, and a composition is controlled suchthat the mole ratios of elements of the high dielectric constant filmare in the following range.0.01≦Hf/(Ta+Hf)≦0.4

Also, a ferroelectric capacitor is disclosed in Japanese Laid OpenPatent Application (JP-A-Heisei 10-294432). In this conventionalexample, the ferroelectric capacitor has the structure in which aferroelectric film is put between a semiconductor substrate and anelectrode. A reaction and/or diffusion barrier film are provided betweenthe semiconductor substrate and the ferroelectric film or between theferroelectric film and the electrode. The barrier film is formed offluoride of at least one alkaline earth metal element selected from thegroup consisting of calcium, strontium and barium.

Also, a high dielectric constant silicate gate dielectric is disclosedin Japanese Laid Open Patent Application (JP-A-Heisei 11-135774). Inthis conventional example, a method of manufacturing an electric fieldeffect device on an integrated circuit includes a step of providing asingle crystal silicon substrate, a step of forming a metal silicatedielectric layer on the substrate and a step of forming a conductivegate on the metal silicate dielectric layer. When the metal silicatedielectric layer is formed, the substrate is cleaned such that pure Siis exposed on the substrate and a first metal film is deposited on theSi surface. The silicide film of first metal is formed on the substrateby annealing the substrate in an inactive environment, and a metalsilicide dielectric layer is formed by oxidizing the silicide layer ofthe first metal. Or, when the metal silicate dielectric layer is formed,first metal and silicon are deposited on the substrate in an oxidantenvironment to form a layer oxidized partially at least, and then anannealing is carried out in the oxidant environment. Or, when the metalsilicate dielectric layer is formed, the substrate is cleaned such thatthe pure Si is exposed on the substrate and a metal silicate havingoxygen vacancies is deposited on the Si surface, and then an annealingis carried out to the metal silicate in the oxygen environment to form ahigh-quality metal silicate dielectric layer.

Also, in this conventional example, a field effect device is composed ofa single crystal silicon semiconductor channel region, and a metalsilicate gate dielectric layer formed on the channel area. The metalsilicate is selected from the group consisting of zirconium silicate,barium silicate, cerium silicate, zinc silicate, thorium silicate,bismuth silicate, hafnium silicate, tantalum silicate and thosecombinations. A conductive gate is provided to cover the gate dielectriclayer.

Also, insulator material is disclosed in Japanese Laid Open PatentApplication (JP-A-Heisei 11-186523). In this reference, the insulatorhas crystal material which contains Ti and in which an atomicconcentration ratio Bi/Ti in Bi₂SiO₅ is equal to or more than 3. Theinsulator film is formed by heating and vaporizing raw materials whichconsist of a metal compound containing Bi and a metal compoundcontaining Ti, and by supplying these vaporized gases onto a Sisubstrate which is kept to a predetermined temperature, at the same timeunder predetermined pressures with an inactive carrier gas and an oxygengas.

Also, a method of forming a semiconductor device and a dielectric filmis disclosed in Japanese Laid Open Patent Application (JP-P2000-323591). In this conventional example, a single crystal siliconlayer is epitaxially grown on a silicon substrate. Bi, Si and oxygen arediffused to form a bismuth silicate film by introducing an oxygen gasand a gas obtained by vaporizing alt-tri-bismuth into a reactionchamber, and by keeping the substrate at a high temperature. Moreover, aBIT film as a ferroelectric substance film is formed on the bismuthsilicate film. After that, after a polysilicon film is deposited on thesubstrate, the polysilicon film, the BIT film and the bismuth silicatefilm are patterned in order. Thus, a gate electrode, a storage sectionand a buffer layer are formed. Deterioration of the characteristic ofMFISFET caused by the erosion of a channel region can be prevented andthe structure near the boundary between the buffer layer and the storagesection becomes good.

DISCLOSURE OF INVENTION

Therefore, an object of the present invention is to provide a highdielectric constant insulating film to improve electricalcharacteristics and thermal stability of the dielectric film and themanufacturing method of the same.

Also, another object of the present invention is to provide asemiconductor device having a metal silicate film as a high dielectricconstant insulating film and a manufacturing method for the same.

In an aspect of the present invention, a semiconductor device includes ametal silicate film as a dielectric film. The metal silicate film has alower portion, a center portion and an upper portion, and a siliconconcentration in the metal silicate film is higher in the upper portionthan the center portion.

Also, in another aspect of the present invention, a semiconductor deviceincludes a metal silicate film as a dielectric film. The metal silicatefilm has a lower portion, a center portion and an upper portion, and asilicon concentration in the metal silicate film is lower in the upperportion and the lower portion than the center portion.

Also, in another aspect of the present invention, a semiconductor deviceincludes a substrate, and a dielectric film directly or indirectly onthe substrate. The dielectric film contains a metal silicate film, andthe metal silicate film has a lower portion, a center portion and anupper portion, and a silicon concentration in the metal silicate film islower in the center portion than in the upper portion and in the lowerportion.

Here, the substrate is a silicon substrate, and the metal silicate filmmay be formed directly on the substrate.

Also, the metal silicate film may be formed on the substrate through atleast one in a polysilicon film, a polycide film and a silicide film.

At this time, it is desirable that the semiconductor device may furtherinclude a doped layer formed on the substrate, and the dielectric filmfunctions as a gate oxide film.

Also, the dielectric film may be formed on the substrate through theinterlayer dielectric film, and the dielectric film may be a capacitiveinsulating film for a capacitor.

In this case, the semiconductor device may further include a conductivefilm formed on a surface on the dielectric film. Also, the metalsilicate film may contact the conductive film. Also, a portion of theconductive film contacting the metal silicate film is desirably formedof one of a polysilicon germanium, a polysilicon, a polycide andsilicide.

Also, a silicon concentration in the metal silicate film may changecontinuously or in a step manner.

The metal silicate film desirably contains one or more elements of thegroup consisting of Zr, Hf, Ti, Ta, Al, Nb, Sc, Y, La, Ce, Pr, Nd, Sm,Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

In another aspect of the present invention, a method of manufacturing asemiconductor device, is achieved by (a) starting formation of a metalsilicate film on a semiconductor substrate by supplying a first sourcegas which contains silicon in a first flow rate, and supplying a secondsource gas which contains at least one metal element in a second flowrate; and by (b) continuing the formation of the metal silicate film onthe semiconductor substrate by changing the flow rate of the firstsource gas from the first flow rate into a third flow rate, and bychanging the flow rate of the second source gas from the second flowrate into a fourth flow rate. A ratio of the first flow rate to thesecond flow rate is larger than the third flow rate and the fourth flowrate ratio.

The method of manufacturing the semiconductor device may further include(c) completing the formation of the metal silicate film on thesemiconductor substrate by changing the flow rate of the first sourcegas from the third flow rate into a fifth flow rate, and by changing theflow rate of the second source gas from the fourth flow rate into asixth flow rate. A ratio of the third flow rate and the fourth flow rateis smaller than the fifth flow rate and the sixth flow rate ratio.

Further, it is desirable to carry out a thermal treatment to the metalsilicate film after the (c).

Preferably, the first source gas is continuously changed from the firstflow rate into the third flow rate and the second source gas iscontinuously changed from the second flow rate into the fourth flowrate. Instead, the first material gas may be changed from the first flowrate into the third flow rate in a step manner and the second materialgas may be changed from the second flow rate into the fourth flow ratein a step manner.

Preferably, the second source gas contains one or more element selectedfrom the group consisting of Zr, Hf, Ti, Ta, Al, Nb, Sc, Y, La, Ce, Pr,Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

In another aspect of the present invention, a semiconductor deviceincludes a semiconductor substrate; a metal silicate film formed on thesemiconductor substrate as a gate dielectric film; and a gate electrodeformed on the metal silicate film. A dielectric constant of the metalsilicate film changes in a thickness direction of the metal silicatefilm, and is the largest on a center portion thereof.

At this time, the metal silicate film has a band gap larger than that ofsilicon, and the metal silicate film may include a lower portion layer,a center layer, and an upper portion layer. It is preferable that theband gap in each of the lower portion layer and the upper portion layeris larger than that of the center layer and the dielectric constant inthe center layer is larger than that of the lower portion layer and theupper portion layer.

The dielectric constant may change continuously or in a step manner.

Also, in another aspect of the present invention, a semiconductor deviceincludes an dielectric film formed on a semiconductor substrate; a lowerelectrode formed on the insulating film; a metal silicate film formed onthe lower electrode; and an upper electrode formed on the metal silicatefilm. A dielectric constant of the metal silicate film changes into athickness direction of the metal silicate film and is the largest in acenter portion.

The dielectric constant may change continuously or in a step manner.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross sectional view showing the structure of asemiconductor device of the present invention;

FIG. 2 is a diagram showing a composition profile of a dielectric filmin the structure shown in FIG. 1;

FIG. 3 is a diagram showing an energy band of a MOS structure that has asilicate dielectric film whose composition is modulated into a directionof a film thickness;

FIGS. 4A to 4 c are cross sectional views showing a method ofmanufacturing a semiconductor device according to a first embodiment ofthe present invention;

FIGS. 5A to 5C are cross sectional views showing a method ofmanufacturing a semiconductor device according to a second embodiment ofthe present invention;

FIG. 6 is a cross sectional view showing the structure of a film formingapparatus used for manufacturing the semiconductor device according tothe second embodiment of the present invention;

FIGS. 7A to 7C are photographs showing observation examples of voids atthe poly-Si/Hf silicate interface; and

FIG. 8 is a graph showing a dependency of a void density on a silicatesurface Hf concentration at the poly-Si/Hf_(x)Si_(1-x)O₂ interface.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a semiconductor device having a high dielectric constantinsulating film of the present invention will be described withreference to the attached drawings.

FIG. 1 is a cross sectional view showing the structure of thesemiconductor device having the high dielectric constant insulating filmof the present invention. A dielectric film 102 is formed on a siliconsubstrate 101, and a polysilicon electrode 103 is formed on thedielectric film 102. A polysilicon germanium electrode may be used inplace of the polysilicon electrode 103. The dielectric film 102 containsa metal silicate film. That is, the dielectric film 102 may be a metalsilicate film as a whole or may have other insulating films in an upperor lower portion. In the following description, the dielectric film 102consists of the metal silicate film.

FIG. 2 is a diagram showing the composition of metal and silicon in themetal silicate film 102. As shown in FIG. 2, in the metal silicate film102 of the present invention, the metal composition has a maximum in acenter portion and becomes the minimum in the lower or upper portion ofthe film. The silicon composition is in the complementary relation tothe metal composition, and has the minimum in the center portion and themaximum in the lower and upper portions of the film. As one example ofthis composition modulated structure, a laminate structure of metaloxide films and a metal silicate film having the silicon compositionmodulation is contained such that the silicon composition is zero in thecenter portion. Also, as another example, a laminate structure is alsocontained of a metal silicate film and oxide films such that the metalcomposition becomes zero in upper and/or lower portions of the metalsilicate film.

When the metal silicate film of the present invention is used as a gatedielectric film, the dielectric constant can be made high in the filmcenter portion of the structure shown in FIG. 2, because the dielectricconstant of the metal silicate becomes high with the increase of metalconcentration. Also, the silicon concentration may increase continuouslyor in a step manner toward the upper and lower boundaries such that thecomposition of the gate dielectric film becomes equivalent to that ofthe silicon oxide film at the interface with a silicon substrate, apolysilicon gate electrode or a polysilicon germanium gate electrode.Therefore, the electrical interface characteristics become similar tothose of the silicon oxide film and the silicon, and it is possible torealize the junction excellent in the electrical interfacecharacteristics compared with the conventional metal oxide film/siliconinterface, or the metal silicate/silicon interface. Moreover, becausethe silicon oxide film has a wide band gap compared with usual highdielectric constant material, as shown in FIG. 3, the band gap extendsat the interface or the neighborhood where the silicon composition ishigh. Therefore, band offset at the interfaces become large, and it ispossible to restrain an electric current component which flows throughthe gate dielectric film even when carriers are excited thermally in thesilicon substrate and the gate electrode.

In addition, according to the silicate dielectric film of the presentinvention, the improvement of the thermal stability of the gatedielectric film is achieved. The crystallization temperature of thesilicate in which the metal composition is high is low relatively.However, as described above, the structure shown in FIG. 1 has alaminate structure in which the layer of a high metal composition is putbetween the high silicon composition layers and has a highcrystallization temperature. Therefore, it is possible to raise thecrystallization temperature of the film center portion having the highmetal composition. As a result, in the MOS structures having a same gateinsulator, the gate dielectric film having the composition modulationstructure of the present invention can realize the more excellentthermal stability compared with a case of the uniform composition.

Moreover, in the silicate dielectric film of the present invention, theinterface characteristics are improved between the polysilicon (poly-Si)electrode (or polysilicon germanium (poly-SiGe) electrode) and the gatedielectric film. Generally, poly-Si (or poly-SiGe) electrode is formedon the high dielectric constant film by an LPCVD method and so on, butvoids are formed at the interface between the poly-Si (or poly-SiGe)electrode and the high dielectric constant film. FIGS. 7A to 7C showobservation examples of such voids. FIGS. 7A and 7B are the sectionalobservation examples by the transmission electron microscope when thepoly-Si film is deposited on the Hf silicate film by the LPCVD method.The composition in the surface of the Hf silicate film isHf_(x)Si_(1-x)O₂ (x≈1.0:HfO₂), Hf_(x)Si_(1-x)O₂ (x≈0.3) in FIGS. 7A and7B, respectively. As shown by the arrows at the interfaces of thesamples, voids with about 30-nm diameter and about 10-nm height areobserved. On the other hand, FIG. 7C is a cross sectional observationexample when a poly-Si film is deposited on SiO₂. Any void is notobserved at the interface of poly-Si/SiO₂ unlike the above examples.Such a void causes depletion at an electrode/high dielectric film. As aresult, the electrical thickness of the gate dielectric increases and amerit by using a high dielectric constant film as the gate dielectricfilm passes away.

It is possible to avoid the formation of the void by employing thestructure of the present invention in which the Si concentration in thehigh dielectric constant film is made high at the interface betweenpoly-Si and the high dielectric constant film. This is because a densityof voids decreases as the Hf concentration in the high dielectricconstant film decreases. FIG. 8 is a graph showing the density of voidsto the surface Hf concentration of the silicate film. The horizontalaxis shows Hf concentration in the % unit. The vertical axis shows thedensity of voids, supposing that a void density when the Hfconcentration is 100% is 1. The void density decreases rapidly as Hfconcentration decreases. As understood from the graph of FIG. 8, if theHf composition in the silicate film is equal to or less than 0.5, thevoids decrease rapidly and it is possible to avoid the devicecharacteristic degradation due to the defects such as the voids and soon at the interface conspicuously. Also, it could be understood that theHf composition is desirable to be equal to or less than 0.3 forrestraining the influence to such a device characteristic as much aspossible.

It should be noted that the case that the electrode is poly-Si isdescribed in the above. However, the structural defects at the interfacebetween the electrode and the high dielectric constant film can berestrained by the silicate dielectric film of the present invention evenin case that a poly-SiGe electrode is deposited on the high dielectricconstant film using a source gas containing a silane, like this poly-Sielectrode.

Also, the case that poly-Si film is deposited on the Hf silicate film isdescribed in the above. However, when the poly-SiGe film is deposited onthe Zr silicate film, the voids are generated at the interface if a Zrconcentration is high and the generation of the void is restrained ifthe Zr concentration is low at the interface. This shows that it is easyfor the voids to generate when a metal concentration is high in thesilicate film surface. Therefore, it could be considered that the samephenomenon occurs when the silicate contains metals such as Zr, Hf, Ti,Ta, Al, Nb, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb,and Lu.

In this way, in the present invention, while eliminating varioustrade-off relations of the composition in the metal silicate film as aproblem in case of application, the improvement of the thermal stabilityis realized at the same time as the improvement of the electricalinterface characteristics and the increase of dielectric constant of thegate dielectric film. Thus, it is possible to provide the highdielectric constant gate insulating film that is desirable in case ofdevice manufacture.

Also, from the same reason as the above, when the metal silicate filmaccording to the present invention is used as the dielectric film of acapacitor that has a polysilicon film as an electrode, the highdielectric constant can be realized while improving interfacecharacteristics, and the thermal stability can be improved.

Therefore, the semiconductor device according to the present inventionhas a structure in which the high dielectric constant film formed ofmetal oxide or metal silicate can be used as the gate dielectric filmfor the capacitor cell, and the silicon composition in the highdielectric constant film is modulated in the direction of the filmthickness. The silicon composition in the gate dielectric film increaseson the junction side of the high dielectric constant film with thesilicon substrate or the polysilicon (the polysilicon germanium)electrode, and the silicon composition in the gate dielectric filmincreases on the junction side with the gate electrode or thepolysilicon (the polysilicon germanium) upper electrode.

Next, as the manufacturing method of the semiconductor device accordingto the present invention, when a film is formed in a CVD (Chemical VaporDeposition) method, a silicon source gas ratio is set high at an initialstage of the film formation, and a metal source gas ratio is set high inthe film formation of the film center portion. After that, the siliconsource gas ratio is again set high at a final stage of the filmformation. It is desirable to carry out thermal treatment after the filmhas been formed, in order to improve the film quality. It is alsodesirable that the thermal treatment is carried out in the oxidizing orinactive atmosphere for 10 sec. to 10 min. at the temperature of 500 to900° C. The film deposition method in which the gas supply ratio ischanged is effective in case that the silicon and metal source gasratios are changed in the formation of gas absorption layers in theAtomic Layer Deposition (ALD) method in which deposition in each layeris carried out every atom or molecule layer, in addition to a continuousCVD film formation.

It should be noted that it is desirable to carry out thermal treatmentafter film formation to improve the film quality. The desirable thermaltreatment condition is in the temperature range of 500 to 900° C. for 10sec. to 10 min. in the oxidizing or inactive atmosphere.

The desirable metal silicate used in the present invention is silicateof metal for high dielectric constant metal oxide, rare earth elementsilicate, and lanthanoid system element silicate, that is, ZrSiO, HfSiO,TiSiO, TaSiO, AlSiO, NbSiO, ScSiO, YSiO, LaSiO, CeSiO, PrSiO, NdSiO,SmSiO, BuSiO, GdSiO, TbSiO, DySiO, HoSiO, ErSiO, TmSiO, YbSiO, andLuSiO.

Next, more specifically, the semiconductor device according to the firstembodiment of the present invention will be described with reference tothe drawings.

FIGS. 4A to 4C are cross sectional views showing the manufacturingmethod of the semiconductor device according to the first embodiment ofthe present invention. First, as shown in FIG. 4A, after the surface ofa p-type silicon substrate 201 is washed or rinsed, a hydrofluoric acidprocess is carried out to remove an oxide film from the substratesurface.

Next, as shown in FIG. 4B, the p-type silicon substrate 201 isintroduced into a reaction furnace, a zirconium silicate film 202 isformed as a gate dielectric film to have the film thickness of 4 nm byusing ZrCl₄ and SiCl₄ as source gases, and H₂O as oxidant. In this case,the flow rate of SiCl₄ is increased and the flow rate of ZrCl₄ isdecreased to 0 in the initial stage and the final stage of the filmformation. Also, in the middle stage of the film formation, the flowrate of SiCl₄ is minimized and the flow rate of ZrCl₄ is maximized.Between the initial stage and the middle stage and between the middlestage and the final stage in the film formation, both or one of the flowrate of SiCl₄ and the flow rate of ZrCl₄ are gradually changed, and asilicate film is formed to mainly have the composition of SiO₂ in theupper and lower film portions, and the composition of Zr_(0.9)Si_(0.1)O₂in the film center portion, such that the composition continuouslychanges between them. After the film formation, the thermal treatment iscarried out at the temperature of 550° C. in the oxygen atmosphere forone minute to improve the film quality. Subsequently, a polysilicon film203 a is formed on the zirconium silicate film 202 to have the filmthickness of 600 nm by a reduced pressure CVD method.

Next, as shown in FIG. 4C, the polysilicon film 203 a and the zirconiumsilicate film 202 are patterned to form a gate electrode 203. Arsenicions are implanted by using the gate electrode 203 as a mask to formn-type doped regions 204 as a source and drain regions.

The capacitance-voltage and current-voltage characteristics in theMOSFET device manufactured in this way were evaluated. As a result, itwas found that the equivalent oxide thickness was 1.5 nm, and that theleakage current flowing through the gate dielectric film was reduced byabout 3 orders of magnitude compared with the silicon oxide film of thesame electrical thickness.

FIGS. 5A to 5C are cross sectional views showing the method ofmanufacturing the semiconductor device according to the secondembodiment of the present invention. FIG. 6 is a cross sectional view ofthe film deposition apparatus (the MOCVD apparatus) used in the secondembodiment. A tantalum silicate film that the composition changes into astep manner is formed for the semiconductor device of the secondembodiment, using the film deposition apparatus shown in FIG. 6.

As shown in FIG. 6, a substrate 3 is located on a substrate stage 2 in afilm deposition chamber 1. Ta[N(C₂H₅)₂]₄ 5 as organic metal source isaccommodated in a babbler 4 and Si[N(C₂H₅)₂]₄ is accommodated in ababbler 6. H₂ gas is supplied into the babbler 4 through a mass flowcontroller 8 a and H₂ gas is supplied into the babbler 6 through a massflow controller 8 c. O₂ gas is supplied to the film deposition chamberthrough a mass flow controller 8 b. Gases in the film deposition chamber1 are exhausted by an exhaust pump 9. According to a flow shown in FIGS.5A to 5C, the manufacturing method will be described. First, aninterlayer dielectric film 303 is formed on the p-type silicon substratehaving an n-type region 302 in the surface region as shown in FIG. 5A. Acontact hole is opened to pass the interlayer dielectric film 303 to then-type area 302. Subsequently, tungsten is embedded in the contact holeto form a conductivity plug 304. A lower electrode 305 is formed throughpolysilicon deposition and polysilicon patterning to contact theconductivity plug 304.

Next, the substrate is located in film deposition chamber shown in FIG.6. After that, a substrate temperature is increased to 400° C. and NOgas is supplied in the flow rate of 50 sccm through the mass flowcontroller 8 b. H₂ gas is supplied in the flow rate of 1 sccm throughthe mass flow controller 8 a, and at the same time, H₂ gas is suppliedin the flow rate of 10 sccm through the mass flow controller 8 c. Thus,a silicon rich layer 306 a is formed to have the film thickness of 1 nm.

Next, the supply flow rate of NO gas through the mass flow controller 8b is kept to 50 sccm, the flow rate of H₂ gas through the mass flowcontroller 8 a is set to 10 sccm and the flow rate of H₂ gas through themass flow controller 8 c is set to 1 sccm. In this way, a metal richlayer 306 b is formed on the whole surface to have the film thickness of2 nm. After that, a silicon rich layer 306 c is formed to have the filmthickness of 1 nm in the same condition as the lower silicon rich layer306 a is formed. In this way, the film formation of the tantalumsilicate film 306 completes.

Next, as shown in FIG. 5C, to improve a film quality, a thermaltreatment is carried out at the temperature of 550° C. in the nitrogenatmosphere for 5 minutes. Subsequently, the polysilicon film having thefilm thickness of 600 nm is formed on the tantalum silicate film 306 bya CVD method, and is patterned to form the upper electrode 307 of thecapacitor.

In the capacitor cell formed in this way, an equivalent oxide thicknessis 2.0 nm and the leakage current flowing through the dielectric film isreduced to about 2 orders of magnitude compared with the silicon oxidefilm.

As described above, the present invention is not limited to them. Aperson in the art will be able to modify the embodiments suitably in therange which does not deviate from the scope of the present invention.For example, the conductive layer formed on the metal silicate film doesnot have to be always the polysilicon film and the polycide film, andthe silicide film and so on may be used. Also, when the silicon (metal)composition changes into the step manner, there may be a plurality ofcomposition change points in each of the upper layer and the lowerlayer. Moreover, the fabrication method can use a method of formingother than the CVD method, e.g. a sputtering method and so on. When thesputtering method is used, the sputtering method using a multi-target(e.g., Zr target and SiO₂ target) is favorably adopted.

As described above, in the metal silicate film of the present invention,the metal composition is high in the film center portion and the siliconcomposition is increased in the lower portion and the upper portion ofthe film. Therefore, according to the present invention, it is possibleto manufacture the semiconductor device having the silicate film of highdielectric constant superior to the silicon oxide film and having theelectrical characteristics and the thermal stability excellent comparedwith the high dielectric constant film of a metal oxide. Also, theMOSFET and the highly efficient capacitance device with high efficiencyand moreover low power consumption can be realized.

1. A semiconductor device comprising: a substrate; and a dielectric filmdirectly or indirectly on said substrate, wherein said dielectric filmcontains a metal silicate film, and said metal silicate film has a lowerportion, a center portion and an upper portion, and a siliconconcentration in said metal silicate film is higher in said centerportion than in said upper portion and in said lower portion.
 2. Thesemiconductor device according to claim 1, wherein said substrate is asilicon substrate, and said metal silicate film is formed directly onsaid substrate.
 3. The semiconductor device according to claim 1,wherein said metal silicate film is formed on said substrate through atleast one of a polysilicon film, a polycide film and a silicide film. 4.The semiconductor device according to claim 2 or 3, further comprising:a doped layer formed on said substrate, wherein said dielectric filmfunctions as a gate oxide film.
 5. The semiconductor device according toclaim 1, wherein said dielectric film is formed on said substratethrough an interlayer dielectric film, and said dielectric film is aninsulating film for a capacitor.
 6. The semiconductor device accordingto any of claims 1 to 5, further comprising: a conductive film formed ona surface on said dielectric film.
 7. The semiconductor device accordingto claim 6, wherein said metal silicate film contacts said conductivefilm.
 8. The semiconductor device according to claim 6 or 7, wherein aportion of said conductive film contacting said metal silicate film isformed of one of a polysilicon germanium, a polysilicon, a polycide andsilicide.
 9. The semiconductor device according to any of claims 1 to 8,wherein a silicon concentration in said metal silicate film changescontinuously.
 10. The semiconductor device according to any of claims 1to 8, wherein a silicon concentration in said metal silicate filmchanges in a step manner.
 11. The semiconductor device according to anyof claims 1 to 10, wherein said metal silicate film contains one or moreelements selected from the group consisting of Zr, Hf, Ti, Ta, Al, Nb,Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.